Adaptive transmissions in wireless networks

ABSTRACT

A network includes an access point using a first protocol and a station using both the first protocol and a second protocol. The station uses the first protocol before a first threshold and a second protocol after the first threshold. A first duration between the second threshold and the first threshold is at least of sufficient length for the station to receive one data packet from the access point and send an acknowledgment. The station transmits to the access point a current clear-to-send packet at a current time during a current exchange based on success or failure of a previous exchange during which a previous clear-to-send packet was transmitted to the access point at a previous time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority toU.S. patent application Ser. No. 12/568,956 filed on Sep. 29, 2009 whichclaims priority to U.S. Provisional Application Ser. No. 61/102,486,filed on Oct. 3, 2008, entitled “Adaptive Scheduling of PS-Poll andCTS2SELF Transmissions in Coexisting Wireless Networks,” the teachingsof which are incorporated by reference herein.

BACKGROUND

The interference of protocols operating in the same wireless mediums,and even on the same wireless device, creates coexistence challenges.Specifically, the out-of-band emission by transceiver may saturateanother transceiver (starvation) and blocking may occur (avalanching).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the accompanying drawings and detailed description,wherein like reference numerals represent like parts:

FIG. 1 illustrates different technologies and their operating bands inaccordance with at least some illustrative embodiments;

FIGS. 2-7 each illustrate a timing diagram in accordance with at leastsome illustrative embodiments;

FIG. 8 illustrates network in accordance with at least some illustrativeembodiments;

FIG. 9 illustrates a method of scheduling transmissions in accordancewith at least some illustrative embodiments; and

FIG. 10 illustrates a device in accordance with at least someillustrative embodiments.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following claims and descriptionto refer to particular components. As one skilled in the art willappreciate, different entities may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In the following discussion and inthe claims, the terms “including” and “comprising” are used in anopen-ended fashion, and thus should be interpreted to mean “including,but not limited to . . . .” Also, the term “couple” or “couples” isintended to mean an optical, wireless, indirect electrical, or directelectrical connection. Thus, if a first device couples to a seconddevice, that connection may be through an indirect electrical connectionvia other devices and connections, through a direct optical connection,etc. Additionally, the term “system” refers to a collection of two ormore hardware components, and the term may be used to refer to anelectronic device or a combination of electronic devices.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims, unlessotherwise specified. In addition, one having ordinary skill in the artwill understand that the following description has broad application,and the discussion of any embodiment is meant only to be exemplary ofthat embodiment, and not intended to intimate that the scope of thedisclosure, including the claims, is limited to that embodiment.

Most mobile devices are equipped with BLUETOOTH, which enables easyaccess to the mobile devices. Besides BLUETOOTH, many mobile devices arealso able to access WLAN networks, WiMAX networks, 3GPP cellularnetworks, etc. While such coexistence of protocols will benefit usersand operators alike, interferences between different technologies makeoptimum simultaneous operations of these technologies difficult.

As shown in FIG. 1, BLUETOOTH (“BT”) and WLAN (in 2.4-2.5 GHz) operateat close or even similar frequency bands. Therefore, coexistence ofthese protocols in the same device creates conflict challenges.Specifically, out-of-band emission by either protocol's radio maysaturate the receiver of the other's radio. For clarity, discussion willbe in the context of BT and WLAN coexistence; however, use of any kindand any number of communication protocols, including those representedin FIG. 1, is within the scope of this disclosure.

WiMAX, short for Worldwide Interoperability for Microwave Access, is atelecommunications technology that provides wireless transmission ofdata using a variety of transmission modes, from point-to-multipointlinks to portable and fully mobile internet access.

A WLAN, short for wireless local area network, links two or morecomputers or devices using spread-spectrum or OFDM, short for orthogonalfrequency-division multiplexing, modulation technology to enablecommunication between devices in a limited area. This technology givesusers the mobility to move around within a broad coverage area and stillbe connected to the network.

BLUETOOTH uses a radio technology called frequency-hopping spreadspectrum, which chops up the data being sent and transmits chunks ofdata over up to 79 frequencies. In its basic mode, the modulation isGaussian frequency-shift keying (“GFSK”).

Ultra-wideband (aka UWB, ultra-wide band, ultraband, etc.) is a radiotechnology that can be used at very low energy levels for short-rangehigh-bandwidth communications by using a large portion of the radiospectrum.

The Global Positioning System (GPS) is a U.S. space-based globalnavigation satellite system.

All cellular phone networks worldwide use a portion of the radiofrequency spectrum designated as Ultra High Frequency, or “UHF,” for thetransmission and reception of signals. The UHF band is also shared withtelevision, Wi-Fi, and BLUETOOTH transmission. The cellular frequenciesare the sets of frequency ranges within the UHF band that have beenallocated for cellular phone use.

IEEE 802.11 is a set of standards carrying out wireless local areanetwork (WLAN) computer communication in the 2.4, 3.6, and 5 GHzfrequency bands.

A station (“STA”) is any device that contains a medium access control(“MAC”) and physical layer (“PHY”) interface to a wireless medium. Anaccess point (“AP”) is any entity that has STA functionality andprovides access to distribution services via the wireless medium forassociated STAs. STAs and APs can be readily interchanged in manycircumstances. The STA and AP communicate by sending packets to eachother. Many types of packets can be sent including the following.

Acknowledgement packet (“ACK”): After receiving a data packet, thereceiving STA will send an ACK to the sending STA if no errors arefound. If the sending STA does not receive an ACK within a predeterminedperiod, the sending STA will resend the data packet.

Request-to-Send packet (“RTS”): The RTS provides an optional collisionreduction scheme. A STA sends a RTS to as the first step in a two-wayhandshake required before sending data packets. The RTS providescollision control management by including a time value (networkallocation vector or “NAV”) for a duration in which all other STAs areto hold transmissions.

Clear-to-Send packet or Clear-to-Send-to-Self packet (“CTS”): A STAresponds to a RTS with a CTS. It provides clearance for the requestingSTA to send a data packet. The CTS provides collision control managementby including a time value (network allocation vector or “NAV”) for aduration in which all other STAs are to hold transmissions.

Data packet: Data packets move information from one point to anotherusing the packet payload to store information. Different types of datapackets contain different quality of service subfields.

Poll packet: Upon determining that a data packet is currently bufferedin the AP, a STA operating in power-save mode transmits a short poll tothe AP, which responds with the corresponding buffered data packet or anACK. If an ACK is sent, the AP responds with the corresponding datapacket at a later time.

Beacon packet (“Beacon”): Beacons are management packets that containcritical network information such as a beacon interval, timestamp,service set identifier, supported rates, parameter sets, capabilityinformation, and a traffic indication map.

Short Interframe Space (“SIFS”): SIFS is the small gap between the datapacket and its acknowledgment. SIFS are found in IEEE 802.11 networks.They are used for the highest priority transmissions, and enable STAswith this type of information to access the radio link first. Examplesof information that will be transmitted after the SIFS has expiredinclude ACKs, and CTSs.

Avalanching occurs when a mobile device is transmitting via a firstnetwork (e.g., Bluetooth) when another network device transmits a packetto the mobile device via a second network (e.g., a WLAN). The mobiledevice will be unable to transmit an acknowledge signal because channelaccess is reserved for transmission via the first network. Consequently,the device transmitting via the second network may conclude that thepacket was lost and reduce the transmission rate of subsequent packets.The longer transmission interval resulting from the reduced rate mayfurther increase the number of collisions with transmissions via thefirst network at the mobile device, ultimately resulting in progressiveperformance degradation (i.e., an avalanche effect).

FIG. 2 illustrates packet transmission. The STA is a coexistence deviceswitching between periods of WLAN operability and BT operability. Forclarity, discussion will be in the context of BT and WLAN coexistence;however, use of any kind and any number of communication protocols,including those represented in FIG. 1, is within the scope of thisdisclosure. The AP uses only WLAN. The STA receives a beacon indicatinga pending data packet for the STA at the AP. After the BT duration, theSTA transmits a poll to notify the AP that the STA is active to receivethe data. Preferably, the AP cannot send any data before first receiveda poll. Upon receiving this poll, the AP replies with an ACK after aSIFS delay. The data packet is sent, and the STA confirms a successfulreceipt with an ACK. In some embodiments, the AP replies to the pollwith the data packet instead of the ACK. Because the AP is restrictedfrom transmitting any data before receiving a poll from the STA, no CTSis needed, and avalanching is avoided.

However, FIG. 3 illustrates a scenario where the AP does not send thedata packet in time. Specifically, transmission of a data packet fromthe AP to the coexistence node could overlap with the second duration ofBT activity. Such overlap could lead to packet drops or avalanching. Toavoid this problem, the coexistence node generates a CTS in order todelay the data transmission until after the BT activity. Specifically,the NAV of the CTS specifies the duration from receipt of the CTS to theend of the next BT duration. The AP sets its NAV counter based on theCTS, and the AP decrements its NAV counter until the counter reacheszero, at which time the STA will begin use WLAN for communication again.As such, the AP can freely send the data packet without collision,blocking, or transmission during BT activity.

The CTS is transmitted after a reception threshold, RxT. The durationbetween RxT and the beginning of the next BT duration is Tmax. Tmax islong enough for the STA to receive one data packet from the AP andreturn an ACK. When the data transmission rate from the AP to the STAvaries, Tmax and RxT vary accordingly.

However, scheduling of CTS transmissions based on RxT could lead tostarvation and avalanching at the STA when there are transmissions withother STAs in the same network. FIG. 4 illustrates a scenario in whichpoll transmission from STA1 cannot begin due to transmissions from STA2,which is not a coexistence STA, and a large Tmax. Because STA1 does notutilize WLAN during BT activity, STA2 and AP are likely to use that timeto transmit. As shown, the first data-ACK exchange between the AP andSTA2 extends beyond first RxT, thus disallowing a poll to be transmittedby STA1. During the second data-ACK exchange, the gap between the end ofthe ACK and the second RxT is too small. As such, the poll will not betransmitted here either, and STA1 could experience starvation.

STA1 can still suffer from neighbor transmissions even aftersuccessfully transmitting a poll. Most APs cannot start datatransmission immediately after sending an ACK in response to thereceived poll. There is often a delay of several hundreds ofmicroseconds before an AP starts the transmission. This delay allows atransmission to start from STA2 in FIG. 5. Because the transmission ofthe data packet from STA2 occupies most of Tmax, STA1 cannot transmit aCTS in time to delay the data transmission from the AP. As such, the APtransmits the beginning of the data packet during the end of BTactivity, preventing STA1 from correctly receiving the data packet.Without receiving an ACK from STA1, AP will retry sending the datapacket. The retry may itself suffer from collision or blocking, whichmay cause other packets to be retried, leading to an avalanche ofdropped packets.

Preferably, the STA and AP are configured such that the AP cannottransmit a data packet to the STA without having received a poll fromthe STA first. In the event that neither an ACK nor a data packet isreceived from the AP in response to a poll, the STA retries the sequenceby transmitting another poll. If the AP sends a data packet in responseto a poll, but fails to receive the ACK acknowledging this data packet,the next poll from the same STA preferably causes a retransmission ofthe last data packet. If the AP responds to a poll by transmitting anACK, then responsibility for the data packet delivery error recoveryshifts to the AP because the data packet is transferred in a subsequentpacket exchange sequence, which is initiated by the AP.

The protection mechanism using CTSs, however, could greatly reduce thechannel utilization because a CTS disables transmissions from all WLANneighbors during not only the following BT activity, but a large portionof Tmax. For example, when the BT radio has voice traffic carried viasynchronized connection packets HV3, a co-existence node generates a CTSonce every 3.75 ms, resulting in a channel utilization of less than 67%because transmissions from neighbors are disabled for at least 1.25 ms.Channel utilization could be worse when CTS based protection is used bymultiple mobile devices associated with the same AP.

As such, transmissions are allowed if there is enough time to transmit aCTS and the poll-ACK handshake as illustrated in FIG. 6. If a CTS issent after RxT, then poll-ACK exchange follows after RxT but before theBT activity. In various embodiments, the exchange occurs during the NAVof the CTS. In a crowded network, the chance that a coexistence nodewins the medium is increased when Tmax is large due to a low datatransmission rate. As such, starvation and avalanching are avoided. Whenthe BT activity ends, as indicated by the NAV, the AP sends the datapacket and the STA responds with an ACK.

Additionally, the transmission time of the CTS is allowed to beadjusted. Preferably, the threshold to begin transmission of the CTS isdefined as (RxT−x). If a failed CTS transmission from a previousexchange leads to a retransmission in the current exchange, x isincreased exponentially. If the CTS transmission from a preciousexchange was successful, x is decreased linearly for the currentexchange. If (RxT−x) is earlier than poll transmission, a CTS istransmitted SIFS time after the ACK sent in response to the poll asillustrated in FIG. 7. If there is no previous exchange data, the CTS istransmitted at RxT. In this way, CTS transmission adapts to trafficloads in a WLAN automatically, and starvation and avalanching areavoided.

FIG. 8 illustrates a network 1000 comprising an AP 1002 and a STA 1004.Communication between the STA 1004 and the AP 1002 occurs in a firstprotocol. The STA 1004 also communicates using a second protocol. TheSTA 1004 uses the first protocol before a first threshold and a secondprotocol after the first threshold, e.g., the first threshold is thebeginning of BT activity. The second threshold is before the firstthreshold, e.g., the second threshold is RxT. A first duration betweenthe second threshold and the first threshold is at least of sufficientlength for the STA 1004 to receive one data packet from the AP 1002 andsend an acknowledgment, e.g., the first duration is Tmax. The AP 1002 isunable to transmit data packets to the STA 1004 without receiving apoll, e.g., power save rules are applied. Preferably, the STA 1004transmits the poll to the AP 1002 during the first duration. If the pollis transmitted before the second threshold, the STA 1004 transmits thecurrent clear-to-send packet slightly before the second threshold, e.g.before RxT.

As explained above, the STA 1004 transmits, to the AP 1002, a currentclear-to-send packet at a current time during a current exchange basedon success or failure of a previous exchange during which a previousclear-to-send packet was transmitted, to the AP 1002, at a previoustime. If the previous exchange was successful, the current time is laterin the current exchange relative to the previous time in the previousexchange by a linear amount. If the previous exchange failed, thecurrent time is earlier in the current exchange relative to the previoustime in the previous exchange by an exponential amount. If there is noprevious transmission, the STA 1004 transmits the current clear-to-sendpacket at the second threshold.

The STA transmits the current clear-to-send packet, before transmittingthe poll, during the first duration. The STA 1004 receives anacknowledgement to the poll during the first duration. A networkallocation vector period of the current clear-to-send packet expires ata third threshold before which the STA 1004 uses the second protocol andafter which the STA uses the first protocol, e.g., the third thresholdis at the end of BT activity. The third threshold is preferably afterthe first threshold.

The AP 1002 transmits a beacon to the STA 1004, the beacon indicating adata packet is available, and the AP 1002 transmits the data packetafter the third threshold. In at least some embodiments, the poll andthe acknowledgement to the poll are sent during the network allocationvector period. In at least one embodiment, the first protocol is WLANand the second protocol is BLUETOOTH.

FIG. 9 illustrates a method 200 beginning at 202 and ending at 214. At204, the success of a previous exchange is determined. Specifically, ifthe previous exchange comprised successful transmission of a previousclear-to-send packet to an AP at a previous time between a STA and theAP. Determination of successful or failure of previous exchange can bedone for example, by listening to the medium in the first protocolbefore switching to the second protocol. Preferably, communicationbetween the STA and the AP occurs in a first protocol, and the AP isunable to transmit data packets to the STA without receiving a poll. TheSTA also preferably communicates using a second protocol. The STA usesthe first protocol before a first threshold and the second protocolafter the first threshold, and the second threshold is before the firstthreshold. A first duration between the second threshold and the firstthreshold is at least of sufficient length for the STA to receive onedata packet from the AP and send an acknowledgment. For example, thesecond threshold is RxT, and the first duration is Tmax.

At 206, if the previous exchange was successful, the current time isdetermined to be later in the current exchange relative to the previoustime in the previous exchange by a linear amount. At 208, if theprevious exchange failed, the current time is determined to be earlierin the current exchange relative to the previous time in the previousexchange by an exponential amount.

At 210, if there is no previous transmission, the second threshold isused as the current time. At 212, a current clear-to-send packet istransmitted to the AP at a current time during a current exchange basedon the determination. Preferably, the poll is transmitted to the APduring the first duration.

FIG. 10 illustrates a device 1004. Preferably, the device 1004 comprisesa computer-readable medium 1098 storing software 1096 that, whenexecuted by a processor 1008, causes the processor 1008 to perform anyof the steps described in this disclosure. Preferably, the device is aSTA comprising a processor 1008, memory 1098 coupled to the processor,and an antenna 1006. The antenna 1006 transmits a current clear-to-sendpacket at a current time during a current exchange based on success orfailure of a previous exchange during which a previous clear-to-sendpacket was transmitted at a previous time.

If the previous exchange was successful, the processor 1008 determinesthe current time to be later in the current exchange relative to theprevious time in the previous exchange by a linear amount. If theprevious exchange failed, the processor 1008 determines the current timeto be earlier in the current exchange relative to the previous time inthe previous exchange by an exponential amount. If there is no previoustransmission, the antenna 1006 transmits the current clear-to-sendpacket at a second threshold.

The antenna 1006 sends and receives packets using a first protocol, andthe antenna 1006 does not receive data packets without transmitting apoll. The antenna 1006 also sends and receives packets using a secondprotocol. The processor 1008 determines a first threshold before whichthe antenna 1006 uses the first protocol and after which the antenna1006 uses the second protocol. The processor 1008 determines the secondthreshold, the second threshold before the first threshold, and theprocessor 1008 determines a first duration between the second thresholdand the first threshold at least of sufficient length for the antenna toreceive one data packet and send an acknowledgment. The antenna 1006preferably transmits the poll to the AP during the first duration.

Other conditions and combinations of conditions will become apparent tothose skilled in the art, including the combination of the conditionsdescribed above, and all such conditions and combinations are within thescope of the present disclosure. Additionally, audio or visual alertsmay be triggered upon successful completion of any action describedherein, upon unsuccessful actions described herein, and upon errors.

The above disclosure is meant to be illustrative of the principles andvarious embodiment of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. Also, the order of the actionsshown in FIG. 8 can be varied from order shown, and two or more of theactions may be performed concurrently. It is intended that the followingclaims be interpreted to embrace all variations and modifications.

What is claimed is:
 1. A network, comprising: an access pointcommunicating using a first protocol unable to transmit data packetswithout receiving a poll packet; and a station communicating using boththe first protocol and a second protocol, wherein the station uses thefirst protocol before a first threshold and a second protocol after thefirst threshold and wherein a first duration between the secondthreshold and the first threshold is at least of sufficient length forthe station to receive one data packet from the access point and send anacknowledgment, wherein the station transmits to the access point acurrent clear-to-send packet at a current time during a current exchangebased on success or failure of a previous exchange during which aprevious clear-to-send packet was transmitted to the access point at aprevious time wherein the station transmits the poll packet to theaccess point during the first duration, wherein the station transmitsthe current clear-to-send packet, before transmitting the poll packetduring the first duration, wherein the station receives anacknowledgement to the poll packet during the first duration, wherein anetwork allocation vector period of the current clear-to-send packetexpires at a third threshold before which the station uses the secondprotocol and after which the station uses the first protocol, andwherein the third threshold is after the first threshold.
 2. The networkof claim 1, wherein if the previous exchange was successful, the currenttime is later in the current exchange relative to the previous time inthe previous exchange, the current time linearly related to the previoustime.
 3. The network of claim 1, wherein if the previous exchangefailed, the current time is earlier in the current exchange relative tothe previous time in the previous exchange, the current timeexponentially related to the previous time.
 4. The network of claim 1,wherein the access point transmits a beacon to the station, the beaconindicating a data packet is available, and the access point transmitsthe data packet after the third threshold.
 5. The network of claim 1,wherein the poll packet and the acknowledgement to the poll packet aresent during the network allocation vector period.
 6. A method,comprising: determining if a previous exchange, during which a previousclear-to-send packet was transmitted to an access point at a previoustime, between a station and the access point was successful; andtransmitting a current clear-to-send packet, to the access point, at acurrent time during a current exchange based on the determination;wherein communication between the station and the access point occurs ina first protocol, the access point unable to transmit data packets tothe station without receiving a poll packet, wherein the station alsocommunicates using a second protocol, and wherein the station uses thefirst protocol before a first threshold and the second protocol afterthe first threshold, and wherein a first duration between the secondthreshold and the first threshold is at least of sufficient length forthe station to receive one data packet from the access point and send anacknowledgment, if there is no previous transmission, transmitting thecurrent clear-to-send packet at the second threshold, wherein the accesspoint is unable to transmit data packets to the station withoutreceiving a poll packet and wherein the second threshold is before thefirst threshold.
 7. The method of claim 6, further comprising, if theprevious exchange was successful, determining the current time to belater in the current exchange relative to the previous time in theprevious exchange.
 8. The method of claim 6, further comprising, if theprevious exchange failed, determining the current time to be earlier inthe current exchange relative to the previous time in the previousexchange.
 9. The method of claim 6, further comprising transmitting thepoll packet to the access point during the first duration.
 10. A device,comprising: a processor; memory coupled to the processor; and an antennawhich sends and receives packets using both a first protocol and asecond protocol; wherein the antenna transmits a current clear-to-sendpacket at a current time during a current exchange based on success orfailure of a previous exchange during which a previous clear-to-sendpacket was transmitted at a previous time wherein the processordetermines a first threshold before which the antenna uses the firstprotocol and after which the antenna uses the second protocol, whereinif there is no previous transmission, the antenna transmits the currentclear-to-send packet at the second threshold, wherein the antenna doesnot receive data packets without transmitting a poll packet, and whereinthe processor determines the second threshold, the second thresholdbefore the first threshold, a first duration between the secondthreshold and the first threshold at least of sufficient length for theantenna to receive one data packet and send an acknowledgment.
 11. Thedevice of claim 10, wherein if the previous exchange was successful, theprocessor determines the current time to be later in the currentexchange relative to the previous time in the previous exchange by alinear amount.
 12. The device of claim 10, wherein if the previousexchange failed, the processor determines the current time to be earlierin the current exchange relative to the previous time in the previousexchange by an exponential amount.
 13. The device of claim 10, whereinthe antenna transmits the poll packet to the access point during thefirst duration.